<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
  .container {
    width: 500px;
    background-color: black;
  }

  .left {
    width: 200px;
    height: 300px;
    background-color: red;
    float: left;
  }

  .right {
    width: 200px;
    height: 200px;
    background-color: green;
    float: right;
  }

  .footer {
    width: 400px;
    height: 50px;
    background-color: blue;
  }

  .clearfix:after {
    content: '';
    display: block;
    clear: both;
  }
  </style>
</head>
<body>
<div class="container clearfix "> <!-- black -->
  <div class="left">left</div> <!-- red -->
  <div class="right">right</div> <!-- green -->
</div>
<div class="footer ">footer</div> <!-- blue -->
</body>
</html>
